1. Technical Field
The disclosure relates to a control system for an internal combustion engine and a control method.
2. Description of Related Art
Japanese Patent Application Publication No. 2006-291823 (JP 2006-291823 A) discloses an emission control system in which a NOx conversion catalyst (e.g., NOx Storage-Reduction (NSR) catalyst), and an exhaust purification filter (e.g., Diesel Particular Filter (DPF)) are mounted, in an exhaust passage of a diesel engine (which may be simply called “engine”) installed on an automobile, or the like. The NOx conversion catalyst stores nitrogen oxides (NOx) contained in exhaust gas. The exhaust purification filter traps particulate matter (PM) in the exhaust gas.
In this type of engine, a fuel addition valve is provided upstream of the NOx conversion catalyst and the exhaust purification filter, and fuel can be added by means of the fuel addition valve. If the amount of NOx stored in the NOx conversion catalyst reaches a predetermined amount, the NOx stored in the NOx conversion catalyst is reduced by the fuel added from the fuel addition valve (NOx aftertreatment). When sulfur components (SOx) are adsorbed on the NOx conversion catalyst, and S poisoning occurs, rich spikes are conducted through intermittent fuel addition from the fuel addition valve. As a result, the sulfur components are removed, and the NOx storage capability of the NOx conversion catalyst is recovered (S regeneration treatment). If the amount of PM deposited on the exhaust purification filter reaches a predetermined amount, the temperature within the filter is increased to a high level through oxidation reaction of the fuel added from the fuel addition valve. As a result, the PM deposited on the exhaust purification filter is oxidized (burned) and removed (filter regeneration treatment).